1. Field of the Invention
The present invention relates to a numerical control grinding machine for precisely grinding a taper portion of a workpiece through pivot movement of a swivel table.
2. Description of the Prior Art
In performing a taper grinding in a numerical control grinding machine, as shown in FIGS. 1 through 3, a workpiece W is rotatably carried by a center 3 mounted on a work head 1 and another center 4 mounted on a tail stock (not shown). The workpiece W is formed with a reference end surface Wa, and a taper portion Wb of a length (a) is formed at a position which is spaced a distance (A) from the reference end surface Wa.
The taper portion Wb is ground with a grinding wheel G, with the workpiece W being held in a state indicated by the phantom line in FIG. 3. The procedure of such grinding will be described hereafter. First of all, the workpiece W held as indicated by the solid line in FIG. 1 is moved to a position indicated by the phantom line in FIG. 1, by moving a traverse table (not shown) toward the left. This feed amount of the traverse table is such a predetermined amount that the reference end surface Wa passes through a position (f) where an end of a feeler F of an end surface measuring device (not shown) is located. This measuring device is fixedly provided on a grinding machine bed (not shown), and the feeler F is movable toward and away from the workpiece W in a radial direction of the workpiece W. The movement of the traverse table causes a pivot P (shown by the broken line) fixedly provided in the traverse table to move the same amount to a position indicated by the phantom line in FIG. 1.
Subsequently, as shown in FIG. 2, the feeler F is advanced toward the workpiece W, and then, a ram 2 of the work head 1, the centers 3 and 4 and the workpiece W are bodily moved toward the right until the reference end surface Wa is brought into engagement with the feeler F. During this time, the traverse table and the pivot P remain at the same positions.
When the end surface measuring device generates a signal upon engagement of its feeler F with the reference end surface Wa, the traverse table is moved a distance (B) toward the left to locate the workpiece W at a position indicated by the solid line in FIG. 3. At this time, the pivot P is also moved the same amount (B) toward the left.
Thereafter, a swivel table (not shown) mounted on the traverse table is pivoted about the pivot P to pivotally move together with the work head 1, the ram 2 and the centers 3, 4 the workpiece W to a position indicated by the phantom line in FIG. 3. In this state, the grinding wheel G is advanced as indicated by the phantom line, whereby the taper portion Wb can be ground.
As described above, in the prior art apparatus, since the axial positioning of the workpiece W is performed utilizing movement of the ram 2, the position of the pivot P is maintained at a predetermined position regardless of any deviation of the axial position of the reference end surface Wa from an ideal axial position. Consequently, when the swivel table is pivoted a predetermined amount about the pviot shaft P which is held at a predetermined position and the grinding wheel G is advanced a predetermined amount to grind the taper portion Wb of the workpiece W, the length (A) (which is required to be precise) from the reference end surface Wa to the starting point of the taper portion Wb can be made constant with respect to all of workpieces machined therein.
However, prior art apparatus uses the work head 1 which is specially designed to axially move the ram 2 carrying the center 3, thereby resulting in an increased cost of production.